1. Field of the Invention
The present invention relates to a mobile communication terminal including a signal-state indicator system and a method for indicating received-signal strength.
2. Description of the Related Art
Radio communication systems include time division multiple access (TDMA), code division multiple access (CDMA), wireless LAN, infrared wireless communication and other various communication systems. Accordingly, services for mobile communication terminals incorporating a radio function including these plural radio communication systems are expanding. The mobile communication terminals generally switch multiple radio communication systems and multiple frequency bands as needed. Thus, a newly devised technique for indicating signal-strength information to users grows in importance.
In mobile communication terminals that transfer information by radio, the signal condition changes every moment under the influence of the position, surrounding obstacles, and movement. Accordingly, received-signal-strength indication is used to give the users the present availability of the terminals: in general, multiple antenna bars are indicated. In a strong signal condition, the number of antenna bars is increased; in a weak signal condition, the number of antenna bars is decreased. A state in which radio communication is unavailable is indicated as “out of range” (e.g., refer to Japanese Laid-Open Patent Application No. JP-A-2002-34077). Terminals incorporating multiple communication systems also include a system in which antennas corresponding to the number of the communication systems are displayed to indicate the respective received-signal strengths (e.g., refer to Japanese Laid-Open Patent Application No. JP-A-2002-44729).
The foregoing techniques disclosed in JP-A-2002-34077 and JP-A-2002-44729 are for notifying users of a received-signal condition that changes every moment under the influence of the position, surrounding obstacles, and movement, not for notification of the signal condition during the switching of communication systems, or frequency bands. The technique disclosed in JP-A-2002-44729 is not for displaying the signal condition during the switching of multiple communication systems with one antenna indicator.
In communication terminals incorporating a control function capable of selectively switching communications in mobile communication systems having multiple radio communication systems or multiple frequency bands (hereinafter, referred to as communication systems), when a specific communication system is continuously monitored but the other available communication systems are not monitored, the signal condition of the system to which the terminal is switched can be known only after the completion of switching.
Therefore, the technique described in JP-A-2002-34077 has the problem that when the signal condition changes greatly before and after switching, the antenna-bar indicator changes significantly when performing switching.
Also, when the signal condition of the system to which the terminal is switched is poor, the terminal again switches the communication system to search for an available communication system making it inconvenient for the user.
Furthermore, the technique described in JP-A-2002-44729 has the problem that the signal condition at the switching of communication cannot be displayed with one antenna indicator making it inconvenient for the user.